Direct interaction theory of production of hypernuclei by meson scattering

A calculation is made, using a direct interaction model, of the differential cross section for the scattering K⁻ +nucleus → π⁻+hypernucleus. Careful attention is paid to the normalisations in order to obtain a reliable estimate of the absolute magnitude for the process. This is of such a size (≈ 10 mb) as to merit experimental investigation.     

Study of clusters and hypernuclei production with the NICA/MPD experiment

Heavy-ion collisions provide the unique possibility to create and investigate hot and dense matter in the laboratory. At the initial stage of the reaction a QGP is formed, while the final stage is driven by the hadronization process and the formation of clusters. The capture of the produced hyperons by clusters of nucleons leads to the hypernuclei formation which is a very rare process at strangeness threshold energies. We report on the first results on the dynamical modeling of cluster formation with the combined PHSD + SACA (Parton–Hadron–Strings dynamics + Simulated Annealing Clusterization Algorithm) model at Nuclotron and NICA energies. The clusters selection in SACA is realized by a simulated annealing procedure to obtain the most bound configuration of fragments and nucleons. Based on present predictions of the combined model we study the possibility to detect such clusters and hypernuclei in the NICA/MPD detector.     

Decay of hypernuclei

We present a nonrelativistic transition potential for the weak strangeness-changing reaction ΛN → NN. The potential is based on a one meson exchange model (OME), where, in addition to the long-ranged pion, the exchange of the pseudoscalar K, η, as well as the vector ,ω, K^* mesons is considered. Results obtained for different hypernuclear decay observables are compared to the available experimental data.     

The formation of hypernuclei by K− capture

K^? capture leading to the formation of hypernuclei takes place with the kaon either in a Bohr orbit (capture at rest), or in flight. We analyze both situations in the framework of the distorted-wave impulse approximation (DWIA), derive cross sections and formation rates, and compare the results with experimental data on the reaction ¹²C(K^?, π^?)¹²_ΛC¹. Corrections to the DWIA which arise from rescattering, from binding energy effects and from the intermediate formation of a ∑-hyperon, are estimated and found not to be negligible.     

Pionic decay of hypernuclei

The mass number dependence of the total pionic decay rate of hypernuclei is evaluated under the closure approximation by using DDHF single-particle wave functions and taking into account the pion distortion and absorption. The effect ofNN andN correlations are then incorporated and found to give a drastic enhancement especially in heavy hypernuclei. More detailed features are discussed for partial and total decay rates of typical light hypernuclei.Presented at the symposium Mesons and Light Nuclei, Bechyn, Czechoslovakia, May 27–June 1, 1985.     

Excited states of hypernuclei

A two-body model of a hypernucleus with realistic N potentials is used to calculate the energies of the excited states of the particle in heavy hypernuclei. The positions of the levels are investigated as functions of: a) the form of the N potential, b) the size of the core nucleus and the form of the nucleon density, and c) the mass number A.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 33–37, April, 1980.     

Light deformed hypernuclei

In the Hartree-Fock scheme, the influence of the added -hyperon is studied on theN= Z even-evenA40 nuclei. The emphasis is put on the shape polarizability, which is related to the bulk properties of the potentials used. Possible experimental connections are commented.Dedicated to Academician Václav Votruba on the occasion of his seventieth birthday.Some of the results have been presented preliminarily at the Balaton 79 Conference on Large Amplitude Collective Motions [35], Discussions with L. Majling, M. Sotona and V. N. Fetisov are greatly acknowledged. Special thanks are due to Miloslav Sotona for constructing Si interactions.     

Structure of light hypernuclei

The structure of light hypernuclei with strangeness S=−1 and −2 is investigated with the microscopic cluster model and the Gaussian expansion method (GEM). We emphasize that the cluster picture as well as the mean-field picture is invaluable to understand the structure of Λ hypernuclei, Σ hypernuclei and double Λ hypernuclei. A variety of aspects of Λ hypernuclei is demonstrated through a systematic study of p-shell hypernuclei (,, , , , , ) and sd-shell ones (, ): for example, the appearance of genuine hypernuclear states with new spatial symmetry which cannot be seen in ordinary nuclei, the glue-like role of the Λ particle which shrinks the size of nuclear core and thus reduces the B(E2) value, and the halo and skin structures in and etc. The typical light hypernucleus is thoroughly investigated, including its production, structure and decay. Precise three-body and four-body calculations of , and using GEM provide important information on the spin structure of the underlying ΛN interaction, by comparing with recent experimental data from γ-ray hypernuclear spectroscopy. The Λ–Σ coupling effect is studied in and . The binding mechanism of is discussed together with the possible existence of , emphasizing the fact that the study of is useful for extracting information on the ΣN interaction differing from that from . A systematic study of double-Λ hypernuclei, constrained by the NAGARA data () within a four-body cluster model indicates that the recently observed Demachi–Yanagi event can be interpreted as the 2⁺ state of . The effect of hyperon mixing in and is investigated using one-boson-exchange potentials and quark-cluster-model interactions for the S=−2 sector. A close relation between nuclear deep hole states and hypernuclei is discussed, emphasizing the selection rule for fragmentation of the s-hole in light nuclei, which is promising for understanding the production mechanism of double-Λ and twin-Λ hypernuclei via Ξ-atomic capture.     

Light hypernuclei in FINUDA

The FINUDA experiment produces Λ-hypernuclei stopping in thin targets the K ^?’s coming from the decay of the Φ particle inside the DAΦNE e ⁺-e ^? collider machine. The Λ-hypernucleus formation is detected by measuring the momentum of the outgoing π^? coming from the strangeness-exchange reaction (K ^?, π^?) inside the targets. Experimental results related to few-body issues, such as hypernuclear spectroscopy, hypernuclear decays, and neutron-rich hypernuclei will be presented.     

Neutron halos in hypernuclei

Properties of single- Λ and double- Λ hypernuclei for even-N Ca isotopes ranging from the proton dripline to the neutron dripline are studied using the relativistic continuum Hartree-Bogoliubov theory with a zero-range pairing interaction. Compared with ordinary nuclei, the addition of one or two Λ-hyperons lowers the Fermi level. The predicted neutron dripline nuclei are, respectively, ⁷⁵ _ΛCa and ⁷⁶ _2ΛCa, as the additional attractive force provided by the Λ-N interaction shifts nuclei from outside to inside the dripline. Therefore, the last bound hypernuclei have two more neutrons than the corresponding ordinary nuclei. Based on the analysis of two-neutron separation energies, neutron single-particle energy levels, the contribution of continuum and nucleon density distribution, giant halo phenomena due to the pairing correlation, and the contribution from the continuum are suggested to exist in Ca hypernuclei similar to those that appear in ordinary Ca isotopes. Received: 21 October 2002 / Accepted: 11 January 2003 / Published online: 8 April 2003     

Doubly strange hypernuclei at PANDA

The FAIR project aims to investigate several fields of physics: QCD, nuclear structure, astrophysics, atomic physics, plasma physics and their applications. In particular, the high-energy storage ring (HESR) will allow high-precision measurements in the antiproton momentum range from 1.5 to 15?GeV/c. Inside HESR, the PANDA experiment will study the charm and strangeness physics, the form factor in the time-like region and other topics like the crossed-channel Compton scattering. The study of the strangeness will be focused onto the doubly strange systems (hypernuclei and hyperatoms) produced with a new technique starting from the antiproton-nucleus reaction.     

Distortion effects in light hypernuclei

We have studied the particle-bound levels in the hypernuclei_Λ ^3,4H,_Λ ⁵He,_Λ ⁸Li and_Λ ^8,9Be in the framework of the full microscopic Resonating Group Method (RGM). In a first step we have solved the respective nuclear many-body problem within the RGM. For each hypernucleus we have then performed a static calculation, in which the nuclear degrees of freedom were kept fixed, and a dynamical calculation in which nuclear degrees of freedom were allowed to vary. The differences between these two studies allowed us to investigate nuclear distortion effects caused by the presence of theΛ-particle. We find the nuclear distortion effects to be inverse proportional to the binding of the nuclear constituents. Thus, the strongest effects are observed for_Λ ³H and for_Λ ⁹Be. Our dynamical approach does not show the strong overbinding of_Λ ³H and_Λ ⁹Be as reported in other cluster model studies. Our results for thep-shell hypernuclei agree reasonably well with those obtained in a semi-microscopic Orthogonal Condition Model (OCM) study which used the same effectiveΛN-interaction as employed in our calculation.     

Studying of hypernuclei with nuclotron beams

The hypernuclear program at Dubna was started in 1988 with investigation of the light hypernuclei production and decay [1]. Nowadays, we are planning to measure lifetime and production cross section of _Λ⁶He and _Λ⁶H hypernuclei.     

Baryon decays and gamma-spectroscopy of hypernuclei

The applicability of (K ^–,^–) - and (K ^–,^– N)-reactions on^13,14C and^14,15N nuclei to the study of -transitions in primary and daughter -hypernuclei is discussed. The intensity of -deexcitation of ¹³C state |S ¹²C(15·11 MeV; 1⁺1): 1/2⁺ has been shown to be comparable with the intensity of baryon decay. Isospin selection rules are used to distinguish excitation energy ranges of primary hypernuclei, where the identification of the secondary -lines is probable.Presented at the symposium Mesons and Light Nuclei, Bechyn, Czechoslovakia, May 27–June 1, 1985.     

Studying of hypernuclei with nuclotron beams

A spectrometer is created to study relativistic hypernuclei produced with beams of accelerated nuclei from the Nuclotron facility (Dubna, JINR). Test runs have been carried out and the conclusion is drawn that the properties of the facility meet the requirements of the task of searching for unknown and studying poorly known neutron-rich hypernuclei. Original Russian Text ? A.V. Averyanov, S.A. Avramenko, V.D. Aksinenko, M.Kh. Anikina, S.N. Bazylev, V.P. Balandin, Yu.A. Batusov, Yu.A. Belikov, Yu.T. Borzunov, O.V. Borodina, A.I. Golokhvastov, L.B. Golovanov, C. Granja, A.B. Ivanov, Yu.L. Ivanov, A.Yu. Isupov, Z. Kohout, A.M. Korotkova, A.G. Litvinenko, J. Lukstiņš, A.I. Malakhov, L. Majling, O. Majlingova, P.K. Manyakov, V.T. Matyushin, I.I. Migulina, G.P. Nikolaevsky, O.B. Okhrimenko, A.N. Parfenov, N.G. Parfenova, V.F. Peresedov, S.N. Plyashkevich, S. Pospišil, P.A. Rukoyatkin, I.S. Saitov, R.A. Salmin, V.M. Slepnev, I.V. Slepnev, M. Solar, B. Sopko, V. Sopko, E.A. Strokovsky, V.V. Tereshchenko, A.A. Feshchenko, T. Horazdovsky, D. Chren, Yu.A. Chencov, I.P. Yudin, 2008, published in Yadernaya Fizika, 2008, Vol. 71, No. 12, pp. 2137–2145.     

Production of hypernuclei with the reaction

We present results on the production of bound states of Θ⁺ in nuclei using the (K⁺,π⁺) reaction. By taking into account the states obtained within a wide range of strength of the Θ⁺ nucleus optical potential, plus the possibility to replace different nucleons of the nucleus, we obtain an excitation spectra with clearly differentiated peaks. The magnitude of the calculated cross sections is well within reachable range.